The present invention relates to organopolysiloxanes, and more particularly to epoxy-functional organopolysiloxanes and to a process for preparing the same.
Heretofore, epoxy containing organosilicon compounds have been prepared by reacting an organopolysiloxane with a dialkali metal salt and thereafter reacting the resultant product with an epihalohydrin. (See U.S. Pat. No. 2,997,458 to Lewis.) Also, U.S. Pat. No. 3,660,434 to Patterson discloses reacting aminosilanes with silanols having terminal double bonds and thereafter reacting the resultant product with epoxide compounds. Organosilicon epoxides are also disclosed in U.S. Pat. No. 3,455,877 to Plueddemann in which these organosilicon epoxides are prepared by reacting organosilicon compounds containing a C.dbd.C group with peracids or by reacting an unsaturated organic compound containing at least one epoxy group with a silicon compound containing at least one SiH group in the presence of a platinum compound.
Also, U.S. Pat. No. 3,563,941 to Plueddemann discloses epoxy silicon compounds which are obtained by reacting a hydroxyl-terminated dimethylpolysiloxane with gamma-glycidoxypropyltrimethoxysilane to form silicon compounds having a methoxy group linked to the same silicon atom as the epoxy group, whereas in the polysiloxane polymers of this invention, the hydrocarbonoxy group is linked to a terminal silicon atom. Moreover, the hydrocarbonoxy group is linked to a different silicon atom than the epoxy group. Thus, the polysiloxane polymers of this invention are more resistant to hydrolysis than the epoxy silicon compounds described by Plueddemann.
Epoxy substituted siloxanes are described in U.S. Pat. No. 3,761,444 to Mendicino, in which lower molecular weight epoxy substituted siloxanes are equilibrated with other siloxanes in the presence of water, a silanol and a basic equilibration catalyst to form siloxane copolymers containing the substituents of both the epoxy siloxane and the other siloxanes.
Johnson et al disclose in U.S. Pat. No. 3,431,143 epoxy-silicones which are prepared by the platinum catalyzed addition of aliphatically unsaturated epoxy compounds to hydrosiloxanes. In contrast to Mendicino and Johnson et al, the polysiloxane polymers of the present invention are branched epoxy containing polysiloxanes.
U.S. Pat. No. 3,887,487 to Camp discloses organosilicon compounds having an oxirane radical bonded directly to a silicon atom which is obtained by the partial or complete hydrolysis of a silane containing an oxirane group and an alkoxy group with conventional silanes, followed by condensation and rearrangement. In the resulant compounds, the alkoxy group and the oxirane radical are bonded to the same silicon atom. In contrast to the copolymers described by Camp, the branched polysiloxane polymers of this invention are more stable to hydrolysis since the epoxy group and hydrocarbonoxy groups are linked to different silicon atoms.
The above described methods for preparing epoxy containing organosilicon compounds have several disadvantages. For example, if a monoepoxy-functional dimethylpolysiloxane composition is desired, the above described methods require a siloxane having a single amino-functional group or one SiH group, or a siloxane which contains one C.dbd.C group. Even though it is known that the aforementioned organofunctional siloxanes can be prepared by equilibration, condensation or cohydrolysis, each process leads to a random distribution of the functional groups. Thus, some of the molecules contain more than one organofunctional group, others contain one, and still others contain no functional groups. Therefore, conversion of the organofunctional group to an epoxide results in the same random distribution. Moreover, some of the methods described in the prior art do not produce epoxy-functional polysiloxane polymers which are resistant to hydrolysis.
Therefore, it is an object of this invention to provide a new class of epoxy-functional polysiloxane polymers. Another object of this invention is to provide a method for preparing branched epoxy-functional polysiloxanes. Still another object of this invention is to provide a method for preparing epoxy-functional polysiloxanes without first having to prepare aminosilanes, vinyl containing siloxanes or SiH containing siloxanes. A further object of this invention is to provide epoxy-functional polysiloxanes which are substantially free from SiH groups and are substantially more resistant to hydrolysis.
The foregoing objects and others which will become apparent from the following description are accomplished in accordance with this invention, generally speaking, by providing epoxy-functional polysiloxane polymers of the general formula ##STR2## in which A is a radical containing at least one epoxy group, R is a monovalent hydrocarbon radical having up to 18 carbon atoms and a is a number of from 1 to 20,000.